TELECOM Digest OnLine - Sorted: Re: Old Party-Line Arrangements

Re: Old Party-Line Arrangements
Mon, 7 Feb 2005 14:51:04 CST

> When it comes to outgoing calls once DDD and CAMA had arrived, I've
> seen references to different ringer wiring combinations to enable the
> equipment to test for originating party, and also in the earlier days
> of DDD that in some places (maybe small independents?) callers had to
> dial an ID digit (e.g. 1x + NPA + number).

The only method I'm aware of for transparently identifying the calling
party was used by Ma Bell on two-party fully-selective lines. This
used the ringer coils in a balanced bridge configuration to ground to
indicate when the "tip" party was off hook.

For four-party and eight-party lines, the usual practice was to
intercept and send the call first to a live operator to identify the

> Can anybody elaborate and explain in more detail the arrangements which
> were commonly used, both in the Bell System and in the larger
> independents?

When speaking in context of Ma Bell, in metropolitan areas, two-party
and four-party fully-selective (no party heard another party's ring)
lines were at times offered. Ringdown voltage was applied between one
side of the pair and ground on two-party lines. On four-party lines a
small cold-cathode tube was used as a rectifier to discriminate the
positive or negative ringdown pulses sent on the appropriate side of
the pair.

Eight party semi-selective lines were offered in rural areas, and in
some cases until quite recently. This was similar to the four-party
fully-selective method but employed a "one long" or "two short" ring
cadence to identify the called party.

The indies would more commonly use frequency-selective ringers to ring
only the bell of the called party's phones.

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